BEagle has the right answer - do all of them! Then all you have to concentrate on is keeping the aircraft in the air!!! Quite a few of the guys of my course were locked away at night studying and looking very nervous during the days they had exams, I saved bricking myself for the flight test
There are plenty of ads in the back of mags advertising ground schools. I did a 2 day groundschool and exams but they expect you to have gone through the books and have a working knowledge which they then build on, you wont manage it if you go in cold.